An exhaust gas recirculation (EGR) is known to be used for preventing the formation of nitrogen oxides during the combustion of fuel in a self-ignition internal combustion engine (for example, a diesel engine). In the EGR at least a portion of the exhaust gas of the diesel engine is recirculated via an exhaust gas turbocharger (for example, exhaust gas turbine) into the internal combustion engine for renewed combustion. This turbocharger drives a compressor and increases thereby the amount of air flow available for combustion. The turbocharger draws energy from the residual pressure of the recirculated exhaust gas and is used to build up a corresponding boost pressure, with the aid of which the efficiency of the combustion and therefore also the performance of the internal combustion engine is improved.
High demands are placed nowadays on such internal combustion engines due to the constant tightening of the legal limits for pollutant emissions. Corresponding limits exist both in the passenger vehicle sector as well as in the commercial vehicle sector.
The EGR facilitates, in particular, a lowering of the oxygen content in the combustion chambers and in the cylinders of the internal combustion engine, as a result of which the combustion temperature in the combustion chamber changes, and the formation of nitrogen oxides (NOx) is thereby reduced.
In the case of diesel engines, particle emissions also come into question, for which legal limits also exist. The particle emissions may be reduced in a known manner with the aid of a particle filter, the particles emitted in the exhaust gas system being eliminated via soot oxidation.
A disadvantage of the EGR in the case of a diesel engine is that the level of particle emissions rises as the proportion of recirculated exhaust gas increases. The principle cause of the higher particle emissions lies in the restriction in the oxygen necessary for the aforementioned soot oxidation. The oxygen content of the exhaust gas reduced by the EGR has a diminishing effect on NOx emissions and an enhancing effect on particle emissions. Accordingly, a conflict exists in diesel engines between the aforementioned soot and NOx emissions, for which a compromise must be found.
Due to existing legal requirements for exhaust gas tests, only limited demands are placed on passenger vehicles in terms of reducing pollutant emissions during dynamic operation of an internal combustion engine, i.e., an operation in which dynamic operating cycles are driven which approach the realistic operational conditions of the internal combustion engine.
Such a dynamic operation requires, in particular, rapid (i.e., transient) changes in torque and rotational speed of the internal combustion engine as well as a reversal of the direction of torque (so-called “coasting”). Thus, modern engine testing stations allow only individual operating points of the engine being tested to be set as stationary, the parameters to be measured, in particular the setpoint values of a corresponding EGR control, usually being cited in a stationary engine characteristic map (for example, torque or engine load over rotational speed). Such an EGR control is based in most cases on an air flow regulation or EGR rate control.
In the commercial vehicle sector, a dynamic operation in the stationary exhaust gas tests performed there is actually completely ignored.
Future statutory regulations, particularly in Europe, the United States and Japan, for certifying an exhaust gas recirculation or exhaust gas after-treatment in both the passenger vehicle and commercial vehicle sectors will constitute a significantly larger component of an aforementioned dynamic test, the emissions forming during actual driving operation (real driving emissions=RDE) and fuel consumption, in particular, being included.